Electrostatic discharge (ESD), which is a large subset of electrical overstress (EOS), is a major reliability issue in integrated circuits (ICs). As semiconductor devices have scaled to smaller dimensions and ICs have become more complex, the potential for destructive ESD events has become more serious. More recently, there has been a tremendous demand for increasing the ESD robustness of Radio Frequency (RF) ICs, especially for wireless applications, such as handheld devices.
ESD protection for Silicon-based technologies, such as complementary metal oxide semiconductor (CMOS) technology, is relatively mature. However, ESD protection circuitry for newer technologies, particularly those involving compound semiconductor materials, such as Gallium Arsenide, is still in its infancy. Compound semiconductor materials are those compounds formed from multiple elements from the periodic table of the elements.
Gallium Arsenide is often used for RF power amplifiers and RF switches because of its intrinsically high low-field electron mobility and breakdown voltage. For RF low noise amplifiers, RF switches, and RF power amplifiers, Gallium Arsenide pseudomorphic high electron mobility transistor (pHEMT) technology may be used. However, ESD protection circuitry for Gallium Arsenide pHEMT technology that is currently in use provides undesirable characteristics. Gallium Arsenide pHEMT ESD protection structures may have unwanted parasitic capacitances and resistances which may adversely affect performance of RF circuits. Ideally, an ESD protection circuit must not affect an input or output signal under normal operating conditions and must not affect the normal operation of the circuit it is protecting. At RF frequencies, the parasitics associated with the ESD protection structures can lead to impedance mismatches, which may cause signal reflection that degrades the performance of the circuit that it is protecting. Thus, there is a need for an ESD protection circuit that has small parasitic capacitance, is linear over a wide frequency range, and can be integrated with other compound semiconductor-based circuits on a single-die.